According to authorities, the teens -- while brandishing a fake firearm -- approached the victim in a stairway near the platform of the North Clybourn station and attempted to forcibly take the victim's iPhone at around 6:30 p.m. Saturday.
Police say the victim was able to run away and ask Spc. Paville Simpson, a military police officer with the Illinois Army National Guard, for help. The armed serviceman was on his way to a job where he works as a security guard.
The serviceman reportedly chased the alleged offenders up the stairs and held them until police arrived.
"I had to help him, because if I can't, who will?" Simpson said. "I swore to. When I took the oath, I said, assist, protect and defend the Constitution against all enemies foreign and domestic."
Simpson, who uses the North and Clybourn station on a daily basis, said he chased the teens upstairs, handcuffed two and got into a scuffle with the third.
"I grabbed him by the collar and asked him where is his gun," Simpson said. "(He) said, I don't have a gun and he went straight for his pocket. I pushed him back and drew my weapon. He's like, 'It's not a gun, it's a lighter. Please don't shoot me.' "
Authorities say they placed the suspects under arrest and recovered a replica firearm. The victim was not injured.
Donte Jackson, 17, is charged with felony attempted aggravated robbery and aggravated assault. Two other teens are also being charged as juveniles. Their names are not being made public.
Simpson received his fellow guardsmen's congratulations all day Sunday, as his heroic actions at the CTA's North and Clybourn Red Line station Saturday evening had become known.
Paville's commanding officer said the 21-year-old exemplifies what if means to be a citizen soldier.
"The actions he took yesterday to help someone demonstrates what a model citizen and a model soldier he is," said Capt. Scott Kozak of the Illinois Amry National Guard. "I wish we had more people like him in this country."